Resting Mechanomyography After Aerobic Exercise

Abstract

A number of mechanisms have been proposed for the elevation in oxygen consumption following exercise. Biochemical processes that return muscle to its preexercise state do not account for all the oxygen consumed after exercise. It is possible that mechanical activity in resting muscle, which produces low frequency vibrations (i.e., muscle sounds: mechano-myographic [MMG] activity), could contribute to the excess postexercise oxygen consumption. Therefore the purpose of this study was to determine whether the resting MMG amplitude changes after exercise, and whether the change is related to the elevation in oxygen consumption (VO2). Ten young male subjects (22.9 yrs) performed 30 minutes of exercise on a cycle ergometer at an intensity corresponding to 70% peak VO2. Oxygen consumption was measured by indirect calorimetry, and MMG by an accelerometer placed over the mid-quadriceps before exercise and for 5.5 hours after exercise. MMG activity, expressed as mean absolute acceleration, was significantly elevated for the 5.5 hours of measurement after exercise (p < 0.05). MMG and VO2 decayed exponentially after exercise with time constants of 7.2 minutes and 7.4 minutes, respectively. We conclude that muscle is mechanically active following exercise and that this may contribute to an elevated VO2.

Effects of spinal anesthesia on resting metabolic rate and quadriceps mechanomyography

“…In fact, early work with an ultra-sensitive EMG with meticulous electrical shielding did show resting-muscle EMG activity (deVries 1965;Jacobson 1943Jacobson , 1951. The correlation of MMG activity with VO 2 (McKay et al 2004) also corroborates earlier work done with these very sensitive EMG systems (deVries et al 1976). Thus, there is EMG as well as MMG evidence for resting-muscle activity.…”

“…Thus, the digitisation rate is well above the critical Nyquist frequency for both signals. The digitised signals were analyzed oV-line on a PC desktop computer, using tested signal analysis programs developed in our lab and described in detail elsewhere (McKay et al 2004). MMG measurements of muscle mechanical activity (Fig.…”

“…MMG is reported as mean absolute acceleration (see McKay et al 2004). The MMG recordings were made on mid-anterior mid-thigh, halfway between the anterior superior iliac spine and the upper pole of patella because it is consistent, horizontal in the supine subject, easy to locate, even in thickset or obese subjects, gives a strong MMG signal because it overlies a large muscle mass, and is paralyzed by spinal anesthesia.…”

“…Exercising muscle results in increased MMG activity and increased oxygen uptake (Stout 1997). Resting muscle also produces MMG activity, and resting-muscle MMG activity is increased after exercise and is associated with the increase in oxygen uptake (VO 2 ) after exercise (McKay et al 1998(McKay et al , 2004(McKay et al , 2006(McKay et al , 2007. Post-exercise MMG activity may therefore contribute to excess post-exercise oxygen consumption, and elevated metabolic rate.…”

Resting mechanomyography before and after resistance exercise

“…The present experiment measures the mechanical activity, using MMG, in resting muscle during states 1 and 4: before (state 1), and after (state 4), vigorous resistance exercise. It follows the format of the study of vigorous aerobic exercise, (McKay et al 2004) but the experimental intervention is vigorous resistance exercise. MMGs were not done in states 2 and 3, contraction and relaxation.…”